The present invention relates to a method for determining boil phases of the contents of cooking utensils on range cook-tops. More specifically, the present invention relates to a method for determining at least one boil phase using an acoustic sensor system.
Boiling water or other fluids or foods (generically xe2x80x9cliquidsxe2x80x9d) is one of the most common uses for a range. It is typically desirable to closely monitor the boil phase of the liquid during such processes, such as, for example, to identify the pre-simmer, simmer onset, simmer and/or boil phases. In this regard, the pre-simmer phase is generally characterized by a calm liquid, and the simmer onset phase is the initial, slow bubbling of the liquid characterized by the appearance of individual bubbles. During the simmer phase, bubbles appear in jets creating the effect commonly referred to as simmering. Finally, in the boil phase, the bubbling of the liquid is generalized, resulting in the familiar turbulence of a boiling liquid. These phases can be identified by experts and experienced cooks. The formation and collapse of the bubbles during the phases create an acoustic signature that changes with the size and number of the bubbles, the rate of their formation, their collapse, and the temperature gradient in the liquid. This acoustic response includes the audible component, which can be easily observed when cooking, as well as responses in various frequency bands. It is also affected by factors including the type of cooking vessel and any ingredients in the liquid.
The boil phase is monitored for a number of reasons. First, many cooking processes require that the liquid be attended to upon identification of a particular boil phase, such as, for example, stirring or adding ingredients. In addition, the boil phase may be monitored to reduce heat after the liquid reaches a boil, either to reduce it to a simmer for cooking purposes or to prevent boil-over. Conventionally, the boil phase is monitored visually. However, such visual monitoring can interfere with the user""s ability to prepare other foods or be otherwise fully productively disposed during heating of the liquid. Also, a busy or inexperienced user may fail to accurately identify a boil phase of interest in a timely manner. Boil-over can result in a burned-on mess or, in the case of gas ranges, extermination of the cooking flame. Moreover, a liquid not monitored upon boiling can boil dry, resulting in burning of the food, damage to cooking utensils or other problems.
Increasingly, in the market for household appliances, manufacturers seek to provide, and consumers desire to have, appliances with a greater degree of automated operation and control. With the increasing affordability of integrating computing power into an appliance, there exists a potential to provide the increased levels of automated control. However, the information gathering tools or devices that will interact with a computer or processor in monitoring or controlling the operation of the appliance must also have desirable cost/performance attributes.
For cooking appliances generally, and for electric, inductive, and gas range cook-tops specifically, automation or partial automation of control of the cooking process, or monitoring of cooking on a cook-top, has traditionally focused on temperature monitoring or sensing. Various temperature sensors have been used for sensing the temperature of a surface heating unit or a cooking utensil positioned thereon, and for controlling the heat input to the heating unit, based upon the sensed temperature. Another form of temperature based sensing is a direct food probe which is inserted into the liquid to measure temperature directly. Such sensors have commonly been used in connection with glass-ceramic radiant cook-tops.
Temperature-based sensing systems for ranges or cook-tops may indirectly or inferentially provide information regarding a boil phase of a liquid contained in a utensil and being heated on the cook-top. However, it is difficult to reliably determine the boil phase since the correlation between temperature and boil phase depends on a number of variables including, but not limited to, the type of liquid, the amount of liquid, any additives, the position of the utensil, and the warping of the utensil. For instance, it is well known that the addition of salt into water raises the boiling temperature. Environmental conditions such as elevation can also affect the temperature associated with boil phases. Finally, the position of the temperature sensor and its calibration can also have a significant impact on achievable accuracy. Therefore, there is a desire for a robust determination of the boil phase that also take into account the cooking modalities, vessels used, various user interactions, and other variations or disturbances in the equipment or environment.
In one exemplary embodiment, an apparatus for determining at least one boil phase of a liquid is provided. The boil phase is determined from an acoustic signal generated by the liquid during heating. An acoustic sensor measures the acoustic signal. The apparatus comprises at least one filter connected to the acoustic sensor. The filter receives and filters the acoustic signal to eliminate excess variation and high frequency noise from the acoustic signal producing a filtered acoustic signal. A derivative estimation filter bank is connected to the filter. The derivative estimation filter bank comprises a plurality of matched filters used to estimate at least one derivative value of the filtered acoustic signal. Each of the plurality of matched filters of the derivative estimation filter bank comprises a first time scale and a first coefficient length. A second derivative estimation filter bank is connected to the filter. The second derivative estimation filter bank also comprises a plurality of matched filters used to estimate the at least one derivative value of the filtered acoustic signal. Each of the plurality of matched filters of the second derivative estimation filter bank has a second time scale and a second coefficient length. A processor is connected to the filter and both the derivative estimation filter banks. The processor identifies the boil phase of the liquid using at least the filtered acoustic signal and the at least one derivative value of the filtered acoustic signal that are provided from at least one of the derivative estimation filter banks.
In another exemplary embodiment, a method of determining at least one boil phase of a liquid is provided. The method measures an acoustic signal generated by a liquid during heating. An acoustic sensor measures the acoustic signal. The method includes filtering the acoustic signal to remove excess variation and high frequency noise. At least one derivative of the filtered acoustic signal is estimated using a plurality of derivative estimation filter banks. Each of the plurality of derivative estimation filter banks has a unique predetermined coefficient length and a unique time scale. One of the plurality of derivative estimation filter banks is used to estimate the at least one estimated derivative of the filtered acoustic signal. The one of the plurality of derivative estimation filter banks is chosen based on the length of time of boiling. The at least one boil phase of the liquid is identified by analyzing the filtered acoustic signal and the at least one estimated derivative of the filtered acoustic signal.